In recent years, from the perspective of environmental preservation, wind farms formed by a group of wind turbine generators which generates power using wind power are becoming popular.
A wind farm is often connected to the grid. In this case, electric power generated in the wind farm is supplied to the grid. The wind farm connected to the grid is required to operate at an appropriate output so as not to disturb the grid stability. Thus, the output of the wind farm is controlled in some cases to achieve a desired output which is specified from the grid side.
For instance, described in Patent Literature 1 is a wind farm control device which is configured to obtain active power to be outputted from the wind farm based on a measurement value at a connection point of the wind farm to the grid and to supply a control signal to each wind turbine based on an external control signal from operators of electric utility.
Although not directly related to the output control for the wind farm, disclosed in Patent Literature 2 is a method for determining a control reserve of each wind turbine by determining a maximum value of the electric variable from the actual value of the wind and subtracting a current value of the electric variable from the maximum value of the electric variable.
Further, a particular output control method is disclosed in Patent Literature 3. According to the method, an operation for limiting the power generation output of the wind farm in advance during the normal operation (a deload operation) is performed, in order to secure electrical output from the wind farm to the grid during gird disturbance.